Which statement about TRH stimulation testing helps differentiate hypothalamic from pituitary dysfunction?

Which statement about TRH stimulation testing helps differentiate hypothalamic from pituitary dysfunction?

• A. TSH rises after TRH administration in hypothalamic dysfunction
• B. TSH fails to rise after TRH administration in hypothalamic dysfunction
• C. TSH falls after TRH administration in hypothalamic dysfunction
• D. TSH remains unchanged after TRH administration in hypothalamic dysfunction

Answer: (B)

TRH stimulation testing works by testing whether the pituitary can respond to TRH when the hypothalamus’s TRH signal may be defective. TRH acts on the anterior pituitary to release TSH. If the hypothalamus is failing to produce TRH (hypothalamic dysfunction) but the pituitary is intact, giving TRH should trigger the pituitary to release TSH, so TSH levels rise. If the pituitary itself is damaged (pituitary dysfunction), it won’t respond to TRH, and TSH will not rise. So, a rise in TSH after TRH administration points to hypothalamic dysfunction, whereas little or no rise suggests pituitary dysfunction.

TRH stimulation testing works by testing whether the pituitary can respond to TRH when the hypothalamus’s TRH signal may be defective. TRH acts on the anterior pituitary to release TSH. If the hypothalamus is failing to produce TRH (hypothalamic dysfunction) but the pituitary is intact, giving TRH should trigger the pituitary to release TSH, so TSH levels rise. If the pituitary itself is damaged (pituitary dysfunction), it won’t respond to TRH, and TSH will not rise. So, a rise in TSH after TRH administration points to hypothalamic dysfunction, whereas little or no rise suggests pituitary dysfunction.